Apparatus for mounting devices on a substrate

ABSTRACT

The invention relates to a method and apparatus which is intended to equip a support substrate with integrated circuit devices of different kinds mounted originally on films. The apparatus includes a machine having cutting heads each associated with the film, and soldering heads. The substrate is mounted on a plate which is movable on a table in a direction perpendicular to the movement of the table, which movement takes place on a threaded spindle drive by a motor. The operation of the machine is monitored and controlled by a unit such as a computer. The invention is applicable in particular to mounting such devices on substrates intended for data-processing assemblies.

This is a division of application Ser. No. 874,652, filed Feb. 2, 1978.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for mountingdevices on a substrate, and in particular for mounting devices such aselectronic integrated-circuit components.

2. Description of the Prior Art

In the modern techniques which are currently employed for producingelectronic equipment and particularly data processing assemblies,increasingly frequent use is being made of integrated-circuitsemiconductor devices, which are not enclosed. These unenclosed devicesare normally referred to as integrated circuit chips. They are generallyrectangular in shape and are provided on at least one of their sideswith output conductors. Such devices ae distinguished on the basis oftheir operational type or the categories into which their dimensionsfall (these dimensions generally being of the order of a fewmillimeters).

In order to make such devices easier to handle, it has been proposed todispose a plurality of these devices at the center of rectangularopenings spaced along a film support. A device is attached to the filmby an array of conductors, each conductor having one of its endssoldered to a contact on the device and its other end attached to anedge of the opening. To remove one of the devices, it is merelynecessary to cut through the conductors in the gap between the deviceand the support film.

Also known is the use of connecting substrates, which frequently takethe form of a board generally made of an insulating material, which isprovided with connecting conductors produced in the form of circuitsprinted on the board. These conductors generally extend from connectingareas disposed adjacent spaces reserved for one type of device andterminate either at similar connecting areas or at out connectingterminals intended to link the substrate to a piece of electronicequipment.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a new and improved methodand apparatus for removing devices in particular electronic components,from their support film and mounting them on a connecting substrate.

In accordance with this and other objects of the invention, the newmethod of mounting devices on a connecting substrate comprises the stepsof (1) placing a first reference system on the substrate with respect towhich are defined a first set of positions of the devices as attached tothe substrate; (2) selecting an appropriate device for each of thesepositions; (3) establishing selectively a second reference systemindependent of the first reference system, with respect to which aredefined a second set of positions of the devices intended to be mountedon the substrate; (4) accurately positioning the substrate in relationto the second reference system; (5) shifting the substrate by alteringthe first reference system relative to the second system so as to alignthe first set of positions on the substrate with the second set ofpositions of the corresponding devices, and (6) attaching to thesubstrate each device which has been positioned on it.

As a result, the mounting apparatus according to this invention is ofthe kind of assembling and mounting devices intended to occupypredetermined positions on a connecting substrate which comprises afirst plurality of predetermined positions, these devices being dividedinto a second plurality of types, and a third plurality of categoriesdetermined by their dimensions. The mounting apparatus includes amovable table having a plate to support the substrate, means forshifting the table and the plate, and cutting and attaching toolsconnected to control means. The control means operates to arrange thetools in at least one line, to assign the devices of each type to atleast one of the cutting tools, to assign the attaching tools to atleast respective ones of the categories, and to effect coupling of thepositioning means on the one hand to the means for shifting the tableand the plate, enabling one of the predetermined positions on thesubstrate to be correctly positioned under the appropriate tool, and onthe other hand to enable the cutting tool to be actuated when thepredetermined position is correctly placed under the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparentfrom the following description, which is given with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a film supporting a plurality ofintegrated-circuit semiconductor devices cooperating with a connectingsubstrate, the figure being intended to illustrate the object of theinvention;

FIG. 2 is a perspective view of an embodiment of the apparatus accordingto the invention, comprising a soldering machine, and a monitoring andcontrol unit;

FIG. 3 is a side view of the apparatus shown in FIG. 2;

FIG. 4 shows an embodiment of a reel-identifying tag according to theinvention;

FIG. 5 is a side, sectioned view of a cutting head according to theinvention, taken along line V--V of FIG. 6;

FIG. 6 is a sectional view taken along line V--V of the head shown inFIG. 5;

FIG. 7 is a front view looking along arrow VII of FIG. 5, andillustrates the systems associated with the cutting head;

FIG. 8 is a partially cut-away perspective view of the U-shaped member,which is associated with the table for supporting the substrate andwhich is intended to cooperate with perforated plates carried by thecutting and soldering heads;

FIG. 9 is a schematic view of the electrical circuit associated witheach photo-electric cell carried by the U-piece shown in FIG. 8;

FIG. 10 is a schematic view of the means for setting up the substrate onthe plate of the machine shown in FIGS. 2 and 3;

FIG. 11 shows a means of defining positions representing the centers ofthe spaces for the semi-conductor devices to be mounted upon thesubstrate;

FIG. 12 shows a slotted abscissa plate resulting from the application ofthe method of definition illustrated by FIG. 11, this slotted platebeing intended to co-operate with the U-shaped member shown in FIG. 8;

FIG. 13 shows a slotted ordinate plate resulting from the application ofthe method of definition illustrated in FIG. 11, this plate beingintended to co-operate with the U-shaped member on thesubstrate-supporting plate;

FIG. 14 is a block diagram of the circuits for monitoring andcontrolling the apparatus shown in FIG. 2;

FIG. 15A shows another example of a connecting substrate to be equippedby means of an apparatus according to the invention;

FIG. 15B shows an external equipping plan for the substrate shown in theFIG. 15A;

FIG. 15C shows an internal equipping plan intended for the monitoringand control unit of the machine shown in FIG. 14;

FIG. 15D shows a non-optimised cutting sequence for the substrate shownin FIG. 15A;

FIG. 15E shows a cutting sequence which has been optimised by themonitoring and control unit;

FIG. 15F shows the cutting path resulting from implementing theoptimised sequence shown in FIG. 15E;

FIG. 15G shows a non-optimised soldering sequence for the substrateshown in FIG. 15A;

FIG. 15H shows a soldering sequence which has been optimised by themonitoring and conrol unit;

FIG. 15I shows the soldering path resulting from implementing theoptimised soldering sequence shown in FIG. 15H;

FIG. 16 illustrates, by way of example, a manner of relating thedesignations for the positions used in drawing up the equipment programsshown in FIGS. 15 and the relative x and y co-ordinates associated withthe substrate;

FIG. 17 illustrates relationships which enable a changeover to be madefrom the relative x axis of the first reference system to the absolute Xaxis of the second reference system for the substrate-supporting table;

FIG. 18 shows an example of the path which will be used to show how theoptimum sequences are defined as this affects the Y axis movements of asubstrate;

FIG. 19 is a general flow-chart for the operation of a machine accordingto the invention;

FIG. 20 is a flow chart related to the drawing up and optimisation ofthe cutting sequence of a machine according to the invention;

FIG. 21 is a flow chart representing the beginning of the cuttingsequence and of the positioning of the tabel, the plate and the films;

FIG. 22 is a flow-chart relating to the advance of the strip and thecheck that the semiconductors devices are satisfactory;

FIG. 23 is a flow-chart relating to the descent of a cutting head;

FIG. 24 is a flow-chart relating to the linking-up and formulation ofthe soldering sequence;

FIG. 25 is a flow-chart relating to the positioning of the table and theplate and the descent of the soldering head;

FIG. 26 is a flow-chart relating to the soldering and the cooling of thesoldered joints;

FIG. 27 is a flow-chart relating to the ascent of a soldering head;

FIG. 28 is a flow-chart relating to the conclusion of operation of themachine; and

FIG. 29 shows the successive positions of the head to which FIGS. 19 to28 relate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The object of the invention is cleary illustrated by FIG. 1 of thedrawings. FIG. 1 shows a connecting substrate 10 having an array ofinternal conductors 12, which are connected to contact areas 14. Aplurality contact areas 14 are disposed about each of the various spaces16, which are each intended to receive a device or component. In thepresent case, this device or component is a semiconductor device 18 of acertain type, which is more generally referred to as a chip. Certain ofthe conductors 12 lead to terminals 20 for external connections whichare intended to be connected into an item of electronic equipment, suchas a data processing assembly for example.

The devices 18 may be classified in two ways. A first way is to considerthem from the point of view of their operational type. As an example,devices 18a and 18'a may be of the first type, whilst chip 18b may be ofa second type. A second way is to categorise the devices 18 by theirdimensions. In the example illustrated, chips 18a and 18b belong tofirst and second categories respectively. It is however possible fordevices of different types to belong to the same category.

Devices 18 of any one type which are intended for placing on thesubstrate 10, are transported thereto by a support member such as a filmor strip 22, which is made from an intensible flexible material. Alongeach of its edges the support member 22 is provided with a series ofequidistant perforations 24, which are symmetrical about thelongitudinal axis of the film 22. In addition, the film 22 supports, inits central portion, a series of rectangular openings 26, around each ofwhich is disposed an array of conductors 28. At the beginning, eachopening is occupied by a device 18 of the same type (type 18a in thepresent case), as shown in openings 26a and 26b. The conductors 28extend beyond the edges of the openings 26 within the film 22, in orderto support the device 18 by respective ones of its ends. A specialfeature of the film 22 is that it incorporates marks associated withthose devices 18 on the film 22, which have not met predeterminedcriteria in an operating test performed beforehand on all the devices 18on the film 22. FIG. 1 shows one of these marks identified by thereference numeral 30. In the example illustrated, the mark 30 is a smallhole made in the edge of the film, between the perforations at thecorresponding edge of the conductors 28 associated with the device 18 inopening 26a. Any other type of mark may of course be used withoutaffecting the principles of the invention. In other words, the device isin opening 26a has been judged unsatisfactory during a test performedbeforehand on the film 22. The operation of the other devices 18 shownin FIG. 1 has been judged satisfactory.

FIG. 1 also illustrates the basic principle of the invention. Using afilm 22, and with reference to opening 26c, the method of this inventioncomprises the steps of shifting the substrate 10 so as to align thecenter of 26c with the center 34 of a space (space 16c in the presentcase), along the axis 32 shown in dotted lines. Device 18'a is thenseparated from the film 22 by cutting the ends of the conductors 28disposed between the device 18'a and the edges of opening 26c, theportions of the conductors attached to chip 18'a being referred to inthe text as the device's external conductors 28'. Device 18'a is thendisposed with in space 16c. As a result of this operation, device 18'awill be disposed in the same way as device 18a in FIG. 1, this latterdevice 18a being assumed to have come from opening 26d in the film 22.Following this step, an attaching tool, such as a soldering tool (notshown) will be pressed against the external conductors 28' to attachthem to the appropriate contact areas 14 associated with space 16c. Thefinal state is demonstrated in FIG. 1 by device 18b, which has itsexternal conductors 28' soldered to the substrate 10.

In conclusion, the foregoing description shows that it is necessary tohave a different film 22 for each type of device 18 required by thesubstrate 10. Consequently, as many cutting tools will be needed asthere are types of devices 18 required for a substrate 10, to enable thedevices to be cut from the corresponding films 22. Conversely, giventhat the soldering is performed by applying pressure and heating theexternal conductors 28' of a device 18, it is only the dimensions of thedevices 18 which determine the number of soldering tools required. Inother words, at least as many soldering tools are required as there arecategories of devices 18, required to equip a substrate 10 with all itsdevices 18. In what follows, the respective centers 34 of the spaces 16on a substrate 10 will be referred to as the "predetermined positions"on a connecting substrate 10.

FIGS. 2 and 3 give an overall view of an apparatus 40 according to theinvention, which is intended to solder the external conductors 28' ofthe semiconductor devices 18 to a connecting substrate 10. The method ofsolder-mounting according to the invention will be described below onthe basis of this apparatus 40. The apparatus 40 comprises a solderingmachine 42 associated with a monitoring and control unit 44 which isdesigned to monitor and control the operation of the machine 42. In thepresent instance, unit 44 is a computer manufactured by the HoneywellInformation Systems Inc. and designed H316. An outline description ofthis unit is given below with reference TO FIG. 14.

The machine 41 illustrated in FIGS. 2 and 3 has a chassis 46, on whichare mounted cutting heads 48 and soldering heads 50 the number of which,in the illustrative embodiment being described, is equal to a maximum often, though other numbers could be selected. The description of FIG. 1showed that the number of cutting heads and the number of soldering headwere functions respectively of the number of types and the number ofcategories of the device 18 required to fully equip a substrate 10. Inthe example being described, it will be assumed that five types ofdevices 18 and four categories of devices 18 are required. Consequently,the machine 42 has to have five cutting heads 48A to 48E, and foursoldering head 50a to 50d. The tenth head 48F is not required and is notinvolved in the normal operation of the machine 42. (For reasons whichwill be given below, it will be assumed that it is a cutting head 48F.

The chassis 46 also incorporates a movable table 52 which carries amovable plate 54 intended to hold a connecting substrate 56 such as thesubstrate 10 shown in FIG. 1. The table 52 moves on a threaded spindle58 which is driven by a motor 60 controlled by unit 44. It is useful forthe motor 60 to be a motor of low inertia such as a DC motor having aflat rotor. Plate 54 moves on a threaded spindle 62 which is driven by amotor 64 controlled by unit 44. It is useful for the motor 64 to be alow-inertia motor such as a DC bell motor (having an iron-free rotor).

Secured to the table 52 is a U-shaped member 66, whose two sides areparallel to the threaded spindle 58 and which is intended to co-operatewith first slotted plates 68 connected to respective cutting andsoldering heads 48 and 50, as will be described below. Similarly, plate54 has secured to it a U-shaped member 70, whose sides are parallel tothreaded spindle 62 and which is intended to co-operate with a secondslotted plate 72, which is fixed to, but detachable from, table 52.

FIGS. 2 and 3 also show that the table 52 moves on two guides 74disposed parallel to the threaded spindle 58 by means of a bearingsystem employing mutually inclined rollers, such systems being wellknown in the art by reason of the stability which they confer on amoving part. Similarly, plate 54 moves on two guides 76 by means of asimilar bearing system. Since spindles 58 and 62 are disposedperpendicular to each other, movement of plate 54 due to driving of onespindle is in a direction perpendicular to the movement of plate 54 whenthe other spindle is driven.

The chassis 46 also includes means for unrolling the films 22step-by-step, these means being formed in the present illustrativeembodiment by ten step-by-step film unrolling devices 78 associatedrespectively with the heads 48 and 50 of the machine 42. The unrollingdevices 78 are of conventional construction and are each driven by asystem provided with a motor 80, such a system being described in U.S.Pat. No. 3,825,161 corresponding to 2,225,977 for example.

FIG. 3 also illustrates the position of the film corresponding to eachcutting head 48. In FIG. 3, the film 22, which is of the kind shown inFIG. 1, is unrolled from a reel 82. The chassis 46 includes ten shafts84 each able to hold one reel 82. Associated with the reel 82 is a tag86 which identifies the reel by means of any desired code and this tagis connected to unit 44. FIG. 4 shows an illustrative embodiment of thetag 86, comprising a common line 88 and seven lines 90 which end interminals 92. The connection or not by a link 93 to the common line 88represents a binary number. The presence of a link may designate binary"0" for example and the absence of a link binary "1". With the tag 86shown in FIG. 4, 126 different types of semiconductor devices 18 can beidentified by the unit 44 to which lines 88 and 90 are connected. Withthis code, it would also be possible for example to indicate theabsences of a reel by the code 0000000 and by the code of 11111111. Inother applications, the code could of course be selected as a functionof the number of types of devices for the purpose of identifying them.Returning to FIG. 3, it can be seen that the film 22 from reel 82 runson various rollers 94. The machine 42 also includes a detector 96, fordetecting the end of the strip 22, which is electrically connected tounit 44.

FIG. 5 is a side, sectioned view of the structure of the cutting head48. Similar heads have already been described in patent applicationsfiled by the present Applicants in France, in particular that bearingthe number 72 39747 corresponding to U.S. Pat. No. 3,887,783. The head48 in FIG. 5 has a substantially rectangular housing 98, which isprovided on one side with a groove 100 intended to be co-operativelyengaged with a rib 102 (FIG. 2) on the chassis 46 of the machine 42 toenable the head 48 to be detachably mounted on the chassis 46. The sideof the head 48 opposite from that bearing the groove 100 contains anopening 104 through which passes a support member 106, which is securedon one side to a slider 108 carrying a cutting tool 110 and on the otherside to a leaf spring 112. The other end of the leaf spring 112 isattached to a transmission member 114, which cooperates with a threadedspindle 116 which is driven by gearing 118 coupled to a DC motor 120.The threaded spindle 116 is coupled to upper and lower stop members 122.The threaded spindle 116 passes through the transmission member 114 andthe latter is prevented from turning to enable the rotary movementproduced by the motor 120 to be converted into a translatory movementalong the axis of the threaded spindle 116. On the side facing member106, the transmission member 114 incorporates pressure detecting meanswhich are formed in the present case by a linear potentiometric sensorwhich, in the example illustrated, has its fixed part secured to piece114 and is connected to a source of voltage (not shown) and its movingpart or contact 126 of the potentiometric sensor, attached to thesupport member 106. Member 106 also incorporates the moving contact 128of a means of monitoring the travel of the tool, which is formed in thepresent case by a linear potentiometer 130 which is attached to thehousing 98 of the head 48 and is connected to a source of voltage (notshown), the moving contacts 126 and 128 are individually connected tounit 44 by means which are not shown. Unit 44 is also electricallyconnected to the motor 120 in order to control it.

The bottom wall of the housing 98 of the head 48 contains a slot 132,intended for a film 22 to pass through as shown in FIG. 3. Under thetool 110, the bottom wall is extended to form a die 134 which will bedescribed below in detail with reference to FIG. 7. A detector 136 isdisposed adjacent the die 134 for checking the quality of the devices,which is intended to co-operate with the holes 30 (FIG. 1) which areformed in a film 22 to indicate that a semiconductor device isunsatisfactory. In the example illustrated the detector 136 is amicro-switch which is actuated by member when the pressure of a gas ispresent to indicate the presence of a hole 30; the means of supplyingpressure to this detector are now shown. The detector 136 is connectedto unit 44 and to the step-by-step unrolling device 78 corresponding tohead 48 to enable it to cause the unrolling device 78 to skip theunsatisfactory semiconductor device 18 and to bring a satisfactorysemiconductor device 18 under the tool 110.

FIG. 6 is an enlarged scale, sectioned view taken along line VI--VI ofFIG. 5. The FIG. 6 shows in detail the way in which the support member106 is guided in the opening 104 in the housing 98 of the cutting head48. Member 106 contains two opposing lateral grooves 138 whichco-operate with respective ones of two other V-shaped grooves 140 in thesides of opening 104. Coupling is by ball-bearings 142 which use theV-grooves 138 and 140 as guides. The slider 108 shown in FIGS. 5 and 6contains a tool supporting member 144 which is made of a mechanicallyrigid material.

FIGS. 5 and 7 show the structure associated with the tool 110. As shownin FIG. 5, the cutting tool 110 contains a central passage 146 which isconnected to an external duct 148 which communicates with a suctionsource (not shown). The purpose of this is to retain the semiconductordevice 18 which has been cut free during the travel of the tool towardsthe substrate 56. This feature is described in the aforementioned Frenchapplication No. 72-39747 corresponding to U.S. Pat. No. 3,887,783.

A system 150 is associated with the cutting tool 110 for positioning thefilm 22 and holding it in position. The system 150 includes two shafts152, which are provided with respective retaining heads 154 andrespective coiled return springs 156, of which one end bears against thelower end of the slider 108. The two shafts 152 are fixed to a bar 158against which the other ends of the springs 156 bear. The bar 158 isintended to press against the film 22, whilst the shafts 152 areintended to be thrust a little way into the perforations 24 in the film,in order to ensure that the position of the film 22 is steady whilst adevice 18 is being cut free. The bar 158 and die 134 are of courseprovided with central holes to allow the tool 110 to pass through. Thedie 134 is also provided with orifices 160 which are intended to acceptthe ends of the shafts 152 and to locate them and the film 22 during thecutting operation.

The soldering heads 50 may be of the same type as the head 48 shown inFIGS. 5 to 7, although in the case of the former, the tool 110 is asoldering tool. In the example being described, the soldering tool isone associated with an electrical heating element. The time for whichcurrent flows can be monitored in a known fashion by means of athermocouple (not shown). It is also possible to add to the head acircuit for cooling the soldered joints by means of nitrogen (notshown). In addition, since the soldering head 50 does not co-operatewith a film 22, it will incorporate neither the slot 132 nor a system150 for positioning the film and holding it in position. Finally, thecutting and soldering heads 48 and 50 are both provided at the bottomwith a rib 162 intended to act as an adjustable seating for a removableslotted plate 68 (FIGS. 1, 8 and 12).

FIG. 8 illustrates the transmitter/receiver system which is associatedwith a U-shaped member 66 co-operating with the slotted plate 68. Itwill be assumed that the plates 68 contain four rows of oblong slots 164(see FIG. 12), each having their major axis parallel to a givendirection (the vertical direction in the drawings). Thetransmitter/receiver system comprises a transmitting device which, inthe present example, is formed by an electric lamp 166 of elongated formwhich is orientated in the given direction (vertically in the drawings),and the length of which is sufficient for it to extend across all fourrows of slots 164. This lamp 166 is mounted in one side of the U-shapedmember 66 and is electrically connected to a source of electrical energy(not shown). The transmitter/receiver system also includes a receiverdevice 168 which takes the form of a panel 170 containing fourphotoelectric cells 172, which are in line with the given direction (thevertical direction in the drawings). Each of these cells 172 has twoadjacent receiving areas 174a, 174b which are separated along a lineparallel to the given direction. The panel 170 is mounted in the otherside of the U-shaped member 66 in such a way that the light beam 176which passes through a slot 164 (a slot in row R4 in FIG. 12) covers theentire length of the areas 174 in the given direction but only a portionof the width of these areas 174.

FIG. 9 is a schematic illustration of the electrical circuit associatedwith each of the cells 172. The areas 174a, and 174b are connected, byconnecting lines 176a and 176b respectively, to the positive andnegative inputs of an operational amplifier 178 which is also connectedto two voltage sources +V and -V. The output of the operation amplifier178 is connected to an energising terminal of motor 60, whose secondenergising terminal is connected to earth. The lines 176a and 176b arealso coupled to the control unit 44, which latter selects the row ofslots which is to be looked at and counts the number of slots in thisrow which pass by, as will be described below.

The positioning of the U-shaped member 66 relative to a slot 164 takesplace as follows. When the light beam 176 impinges in a random fashionon the two areas 174a and 174b , the areas generate electrical currentswhich are of different respective values. The difference between thecurrents results, via operational amplifier 178, in motor 60 beingenergized to drive the table 52 and the U-shaped member 66 in adirection which depends on the sign of the difference between thecurrents. In this way, the table 152 and the U-shaped member 66 willcome to a halt when areas 174a and 174b are receiving equal luminousfluxes and emitting electrical signals of equal magnitude.

The plate 54 is positioned by means of a U-shaped 70, which has atransmitter/receiver system similar to that of U-shaped member 66. Itsphotoelectric cell similarly connected by operational amplifiers to themotor 64 driving the plate. Similarly, the U-shaped 70 will stop at aslot in the plate 72 determined by unit 44.

A description will now be given of the means for positioning thesubstrate 56 on the plate 54 of the machine 42. FIG. 10 illustratesthese means. Before these means are described, it should be mentionedthat the positioning of the substrate 56 takes place with reference to asystem consisting of three selected points 180a, 180b and 180c at theperiphery of the substrate 56. In order better to bring out one of thefeatures of the invention, the irregularity of the edges of thesubstrate 56 is exaggerated in FIG. 10. The three points 180a to c arethree points at these edges which have been defined in relation to agiven reference system so that, when transposed into a similar referencesystem, the substrate occupies precisely the same position as that whichwas defined with reference to the original reference system. In the caseof FIG. 10, this reference system is formed by three rollers 182a, 182b,and 182c which are free to pivot on fixed shafts. When substrate 56 isin place, the points 180a, b and c should correspond with points on theperipheries of rollers 182a, b, and c respectively. This is a convenientmeans of reproducing the position originally selected. To set up thesubstrate 56 in this way and hold it in position, three other rollers184 are provided, these rollers 184 being free to rotate on respectiveshafts which are able to move in slots 186. By withdrawing the rollers184, the substrate 56 can be inserted between rollers 182 and 184 and amechanical system (not shown). When released, the shafts of rollers 186move towards rollers 182, thus automatically positioning the substrate56. FIG. 10 shows an intermediate stage of this positioning operation.From FIG. 10, it can be seen that the movement of the long edge of thesubstrate 56 in response to the pressure from rollers 184, will causethe rollers 182 to turn as dictated by the irregularities. It should bementioned that if the rollers 182 were pegs incapable of rotation theedges would rub against them. Depending upon the irregularitiescountered, the frictional forces would be more or less pronounced andwould hamper the movement of the substrate 56. In addition, there wouldbe a danger of removing material from the irregularities, which mightdetract from the accuracy with which the substrate 56 needs to bepositioned. The use of movable rollers solves all of these problems.Once the substrate 56 has been positioned on the plate 54, it is held inposition by a suction system (not shown) which acts from below thesubstrate 56.

Now that all the details of the structure of the machine 42 has beendescribed, the operation of the machine will be described with referenceto a particulate substrate, which is given solely by way of example. Itwill be recalled that reference numeral 34 was used for the centers ofthe spaces reserved for each device 18 on the substrate 10 shown inFIG. 1. In the case of the substrate 56 which is shown in FIG. 11, thecenter 34 of these areas are identified by reference relativeco-ordinates) relating to a first reference system which is defined inthe example being described, where the co-ordinates are cartesian, bytwo mutually perpendicular axes Ox and oy which represent two adjoiningedges of the substrate 56. In this way the centers 34 may be defined bythe points of intersection of pairs of lines parallel to these axes. Forreasons which will become clearer at a later stage, the substrate 56 isdivided into four rows (also referred to as "corridors") R1, R2, R3 andR4, and four columns C1, C2, C3 and C4, the centers 34, thus eachoccupying a single box defined by a column and a row. For conveniencewhen discussing the positions 34, they will hereafter be referred to bythe letter P followed by the figures for their columns and rows. In eachbox, the positions (centers 34) are defined by the points ofintersection of two line-segments parallel to the axes. The horizontalsegments are marked by the letter H followed by the same references asare used for the corresponding positions, and the vertical segments bythe letter V plus the corresponding references. As an example, positionP44 has corresponding segments H44 and V44. The slots in the plate 68are formed by using the vertical segments V as a basis as shown in FIG.12. The length of the slots is of course independent of the length ofthe segments V. Similarly, slots in plate 72 are formed by using the Hsegments, as illustrated in FIG. 13.

The types of devices 18 intended for the substrate 56 are thendetermined as a function of the respective positions P of the devices 18to be mounted upon the substrate 56. It was assumed above that fivetypes of devices were needed to equip the substrate 56, which called forfive cutting heads 48A to 48E. It was also assumed that these five typesrepresented four dimensional categories, requiring there to be foursoldering heads 56a to 56d. The table below gives an example ofcorrespondences between the positions P and the types and categories ofthe devices 18 to be positioned on the substrate 56. The cutting andsoldering heads 48 and 50 are referred to by letters corresponding tothe types and categories.

    ______________________________________                                        Type      Category      Positions                                             ______________________________________                                        A         a             P.sub.14 P.sub.34 P.sub.42                            B         b             P.sub.11 P.sub.13 P.sub.24 P.sub.44                   C         a             P.sub.32                                              D         c             P.sub.21 P.sub.22 P.sub.33 P.sub.43                   E         d             P.sub.23 P.sub.41                                     ______________________________________                                    

In this example it is assumed that types A and C are of the samecategory a.

To produce the machine 42, a second reference system (absoluteco-ordinates x, y) is established which is independent of the firstreference system and with reference to which are defined the positionsof the devices 18 intended to be mounted on the substrate and the pointswhere soldering is to take place. In the machine 42, the devicepositions correspond to the axes of the cutting tools of heads 48A to48E and the soldering points correspond to the axes of the solderingtools of the heads 50a to 50d (FIG. 2).

In the present embodiment, the axes of the cutting tools are arranged ina first straight line, and the axes of the soldering tools in a secondstraight line which coincides with the first. As can be seen in thedrawings, the cutting and soldering tools lie along a line parallel tothe threaded spindle 58 for moving the table 52. In the present case,this also corresponds to a direction parallel to the axis Ox definedabove by the substrate 56 (FIG. 11) when the substrate is mounted on theplate 54 in the way shown in FIG. 10. The slotted plates 68 are alignedin this direction.

It is now a simple matter to explain the operation of the machine 42.First of all, the substrate 56 is set up on the plate 54 in an extremelyaccurate fashion, as shown in FIG. 10. In the example illustrated, thismeans that the substrate 56 is disposed in such a way its x-axis isparallel to the common line of alignment the cutting and solderingtools. At the beginning, the table 52 and the plate 54 also occupyabsolutely precise positions (Xo, Yo) relative to the line of alignmentof the tools. This position is determined by unit 44 as indicated below.

With the table 52 and the plate 54 in the starting position (Xo, Yo),the units 44 bring the motors 60 and 64 into operation to position thesubstrate 56 correctly under the tool of head 48a. Assuming that thetypes and categories which appear in the table above correspond torespective ones of the heads shown in FIG. 2, unit 44 will operate themotor 60 and 64 in such a way as to line up the axis of the tool of head48a with, for example, position P14, as shown in FIG. 11. The table 52and the plate 54 then adjust themselves respectively to the slot V14 inthe plate 68 associated with head 48A and to slot H14 in plate 72, inthe fashion which was described above with reference to FIGS. 8 and 9.The slots are known to unit 44, which has been provided with details ofthe first reference system, the types and categories of semiconductordevices 18 to be used, the correspondence between the positions P andthe types and categories, and the arrangement of the heads relative toone another. Assuming that the plate 68 for head 48A takes the formshown in FIG. 12, unit 44 selects the first slot in the complete row R4formed by a line of plates 68. After bringing the substrate 65 to a haltwith position P14 on an axis similar to axis 32 in FIG. 1, unit 44actuates head 48A to cut the device 18 from the film 22A (for devices oftype A). The operation of the head 48A will be described further on.When the device 18 has been disposed at position P14, unit 44 thenselects position P34 (see the above table), for example, and operatesmotors 60 and 64 accordingly. Positions P34 (the third position in thepresent case) is selected by unit 44 by counting the slots in row R4 inplate 68, whilst the ordinate position remains the same. After all theoperations involving head 48A have been performed, the table 52 and theplate 54 position themselves relative to the head 48B in conformity withthe above table. This involves shifting the substrate 65 and the firstreference system in relation to the line of alignment of the tool whichdefines the second reference system, in order to line up each positionwith the corresponding semiconductor device 18. Once the substrate 65has received its last device 18 from head 48A, it then passes under thecorresponding soldering heads 50. Head 50a for example, which is of thecategory a, will operate at positions P14, P34, P42 and P32.

The substrate 56 is sub-divided into rows and columns of the x and yaxes, as shown in FIG. 11. If this subdivision were not made, plate 68for example could contain a series of slots 164 occupying the entirewidth of the plate. As a result, the slots corresponding to linesegments V34 and V32, for example, would be very close together, andthis would upset the positioning of the substrate 56 and theservo-control of the motors. By virtue of the subdivision shown in FIG.11 for example, the slots in each row are sufficiently far apart for theservo-control to be satisfactorily operated and to allow the substrate65 to be properly positioned.

The operation of a head 48 will now be described with reference to FIGS.5 to 7. When a desired position P on the substrate 65 is on the axis 32of the tool 110, unit 44 operates the motor 120 to cause transmissionpiece 114 to descend together with, via leaf spring 112, the tool 110.The travel of the tool 110 is represented in FIG. 5 by an arrow 88 whoseorigin 190 is situated at the lower level of tool 110 when the latter isin its initial raised position. A mark 192 corresponds substantially tothe plane of the array of the conductors 28 on the substrate 22 (FIGS. 1and 7). Between 190 and 192, the tool 110 does not encounter anyobstacles and the leaf spring 112 is thus under a normal stress of amagnitude which is indicated electrically by the moving contact 126 ofpotentiometer 124. At the same time, the movement of piece 114 isindicated electrically by the moving contact 128 of potentiometer 130.The positions 190 and 192 are shown close to potentiometer 130 in FIG. 5by the corresponding positions of its moving contact. Consequently, overthe predetermined interval 190 to 192, unit 44 monitors the stress onleaf spring 112 by means of potentiometers 124 and 130. When the toolreaches level 192, it comes into contact with the conductors 28 whichare attached to a device 18, whilst a drop in pressure is brought aboutin passage 146. The force of impact of the tool against the conductors28 is reflected via leaf spring 112 at moving contact 126 and istranslated into an electrical value by potentiometer 124. Unit 44, whichknows position 192 from potentiometer 130, is in a position to evaluatethe magnitude of the force of impact. If for example such a force hadbeen produced in the interval 190 to 192, the impact force would havebeen considered as a fault on the part of the machine and would havecaused head 48 to be stopped. Similarly, unit 44 recognises the force ofimpact at level 192, and is advised of its magnitude by potentiometer124. Means are provided in unit 44 to compare the magnitude of thisforce with a predetermined upper-limit value. Should the force of impactexceed the limit value, unit 44 would consider the force of impact to bea fault on the part of the apparatus and would stop head 48 fromoperating. Between level 192 and the level 194 representing the upperface of substrate 56, the tool descends with its device 18 heldsuspended from it by means of the reduced pressure in passage 146. Thetravel involved as detected by potentiometer 130 and the pressure ismeasured by means of potentiometer 124. In this case too the unit makesthe same checks on pressure. When unit 44 knows from potentiometer 130that the tool has reached the level 194 representing the upper face ofthe substrate 56, the reduced pressure in passage 146 ceases in order todrop the chip 18, whilst unit 44 returns the tool 110 to its originalposition 190. At level 194, it also checks the force with which the toolpresses against the substrate.

The soldering heads 50 may be similar to the heads 48 with tool 110 andits passage 146 replaced by a soldering tool associated with leads forsupplying power to the electrical soldering heating element. When thisis the case, level 192 no longer has to be allowed for. The solderingoperation may be performed by a thermocouple associated with thesoldering tool 110, or as a function of the time for which the solderingcurrent is applied.

The unit 44 will now be described. The above description has set out thefunctions by which it monitors and controlls the operation of themachine 42. Unit 44 is also provided with a program for optimizing theperformance of the machine 42, by selecting the way in which theoperating sequences succeed one another and by reducing to a minimum theamount of time they take. In other words, unit 44 calculates theshortest path to assemble a given substrate in a minimum time. It doesso on the basis of a plan for assembling the substrate 65, asillustrated by FIG. 11 and the above table, on the basis of thearrangements of the heads 48 and 50, and on the basis of monitoring datawhich the unit 44 at all times receives from machine 42 (the pressureexerted by the tools, whether the semiconductor devices 18 aresatisfactory, whether the end of the film 22 has been reached, etc.).If, for example, in the course of an operation the detector 96 fordetecting the end of the strip 22 should make such a detection, theprocess would continue while the operator was replacing the film 22,either on the appropriate head or on another head such as head 48F whichhad been kept in reserve.

FIG. 14 is a block diagram of the apparatus 40 as controlled by unit 44.FIG. 14 shows the principle components of the unit 44 operating inrelation to machine 42. In block form, unit 44 considers unit 42 asbeing formed by a monitoring block 196 connected to the mechanicalassembly 198 of machine 42, this assembly comprises in particular of thecutting and soldering heads 48 and 50, the means for shifting thesubstrate 65, the means for advancing the strips 22 and so on. As forunit 44, it was stated above that it was formed in essence by thecomputer H316. In FIG. 14, this computer is represented by a cabinet200. This cabinet contains a power supply block 202 connected to a desk204 which communicates with an interface block 206 which acts as aninterface between unit 44 and machine 42. The interface block 206communicates with a memory block 208 which, in the example illustrated,has a capacity of 8K words. The monitoring and control block 196communicates with the desk 204 and the interface block 206, and viceversa. The memory block 208 receives from a tape reader 210 informationrelating to the equipment plans for the substrates, represented by block212, and information relating to the monitoring by calculator 200 of theoperation of machine 42, this information being represented by block214. This monitoring is performed by means of a programme which will betermed the "monitor" in what follows. The memory block 208 is also incommunication with a teleprinter 216. In addition, a tape perforator 218receives from the memory block 208 information for safeguarding themonitor, this information being represented by block 220.

Before describing the manner in which the process is monitored by thecomputer 200, the operation of the machine from the operater's point ofview will now be described. The operator first of all ensures that themachine 42 is loaded with reels 82. No specific station is alloted for agiven type of device. The operator is under no obligation, beforestarting the process, to check that all the types of chip required arepresent, that the numbers available are adequate, that the devicesavailable at a station are compatible with the type of cutting head atthe station, or that all the soldering heads required are present. Theoperator then places the substrate, which is to be equipped, on plate54. He feeds in the type of substrate using the teleprinter 216 andinitiates the process. From this moment the operator will have no moreto do except in case of accident. Any action taken by him will howeverstill be monitored by the computer 200.

The computer 200 extracts from its memory 208 the plan for equipping thesubstrate to be equipped, checks whether all the types of the devices 18required are present by means of tags 86, determines the shortest pathwhich the table 52 will have to follow, and starts the process. Thesubstrate is equipped as described above.

With the machine described above, it takes approximately ten minutes tomount the devices 18 upon substrate having sixty-four positions, duringwhich time the operator normally does not participate in the operationof the machine. However, it is possible for the operator to interruptthe automatic process of equipping a substrate at any time during itscourse. This interruption is however monitored by the computer 200 sothat the process can be resumed and finished in the normal way. Asstated above, the process is monitored by the computer 200 by means of aprogram termed the monitor. The general organization of this program anddetails of how it is put into effect appear in the flow charts shown inFIGS. 19 to 29, which form part of the text of the specification.

Regarding the general organization of the monitor program, the equipmentplans are fed into the monitor program, either "on line" from theteleprinter 216 in the case of occasional simple plans, or individuallyfrom punched tape for use in sequence, or collectively from punched tapevia tape reader 210 so that the computer 200 can assemble a file ofequipment plans. The section of the memory block 28 not used by themonitor program is set aside for such a file. Approximately fiftyequipment plans for substrates having sixty-four positions may be storedthere. Loading such a file takes only approximately thirty seconds andcan be done independently of the loading of the monitor program. Underproduction conditions, it is obviously the third method of feeding inequipment plans which will be used as a rule.

The machine is capable of being operated in a first or main mode tomount or equip substrates with devices 18, or a second or service mode;the up-dating in the monitor program of a table containing therecognised types and categories of device and the associated types ofcutting and soldering heads, which table is used when checking thefeasibility of the equipment plan and when drawing up the equipmentsequences; printing out the state of this table; printing out a list ofequipment plans contained in the memory file; printing out the state ofthe machine 42, the kinds and categories of devices 18 and the kinds andcategories of cutting heads 48 and the welding heads 50 present, and thestate of the reels; and finally safeguarding the monitor program, thisoption enabling the monitor to be preserved in its current state in theform of a self-loading punched tape, in particular after the table ofdevices and heads has been up-dated or the parameters of the processhave been altered.

With regard to the tasks performed by the monitor program, the listbelow presents a summary of the operations which are described ingreater detail in the flow-charts shown in the accompanying drawings(FIGS. 19 to 29). Before starting the main mode of operation, themonitor program:

calls up the equipment plan (from the memory file or from outside).

checks the general state of the machine 42,

checks whether the types of devices 18 required are present (which typesneed not be mounted in the machine 42 in any specific way),

checks for compatibility between types of devices 18 and types ofcutting head,

checks that the requisite soldering tools are present (which tools neednot be mounted in any specific way in relation to one another),

indicates to the operator any corrective action to be taken and monitorsthis action,

and determines a sequence for equipping the substrate which minimisesthe time taken to do so, given that equipment the plan may be given inany order and allowing for the siting of the tools.

Whilst the main mode of operator is carried out, the monitor programperforms the following steps:

(1) In the cutting phase:

effects and monitors the XY movements of the table 52 which bring theposition P to be equipped under the requisite cutting head 48,

checks the state of the supply reel, warns the operator if the reelbecomes empty, and if necessary re-optimises the cutting sequence in theevent of a change of reel 82,

simultaneously with the movement of the table 52, it causes the film 22to be advanced until a satisfactory device 18 is reached.

checks the descent of the cutting tool 110, the suction on the device 18which is cut free, the tool's arrival against the substrate with amonitored force, and then the ascent of the tool 110,

and links up with the next cutting and positioning operation.

(2) It automatically links up the cutting phase with the solderingphase.

(3) In the soldering phase it:

effects and monitors the X, Y movements of the substrate which bring thedevice 18 to be soldered under the requisite soldering tool,

controls the descent and drafts the tool in a position against thesubstrate with a monitored force,

monitors the welding of the device 18 with reference either totemperature or time, with these parameters depending upon the type ofsoldering tool employed,

monitors the cooling of the soldered joints and then the upward movementof the tool,

links up with the next soldering operation.

(4) It keeps a permanent watch on the safety functions of the machine 42(that suction is present, that there are no excessive strains on thetools, that the electrical soldering generator is in a satisfactorystate) and intervenes in case of incident to warn the operator andinform him of the corrective action which needs to be taken, and thenmonitors this action.

At this end of the equipping process, it returns the substrate to theloading point, links up with the next job, and increments the film 22.

Reference will now be made to the flow-charts shown in FIGS. 19 to 28.

FIG. 19 illustrates the general flow-chart of the operations performedby the monitor program.

Firstly, the monitor program is initialised and the working option isasked. The service options are verified and, whether not, the operatoris advised. "T" denotes the end step of the program. When the serviceoptions are all checked and satisfied, the step of equipping starts. "A"denotes the beginning of this step, which is described in greater detailin the following flow-charts shown in FIGS. 20 to 29. The type ofsubstrate and the equipping plan are called up. The equipping plan canbe internal, external or on-line. Then, the substrate is equippedaccording to the selected plan. "M" denotes the beginning of the step ofequipping the substrate. When the equipment is ended, instructions aregiven by the operator: if a new substrate of a same type is to beequipped with a same plan, the program is set again to M; if a substratehaving a new type is given, the program returns to A since this type hasto be specified together with the corresponding equipment plan; and ifno substrate is provided, the program is regarded as finished andreturns to T.

FIG. 20 to 28 are connected to one another by the characters A-M and Tand specify the step of equipping the substrate.

At A the type of substrate and then the equipping plan are called up. Asurvey of types of device and head present is made. The program thensuccessively checks for the presence of types of device needed, for thedevice/head compatibility and for the presence of soldering headsrequired. Any corrective action is indicated to the operator and theprogram is called to make new survey and checks. If these operations aresatisfied, the step concerning the equipping plan is ended and theprogram starts the cutting sequence.

Firstly, the cutting sequence is optimized, for example in the mannerwhich will be described herebelow. Then (see FIG. 21) the substratesetting up and start are called up. Upon the end of these operationsmade by the operator, the program controls the start. If the start isassurized, the initial conditions are checked (for example: toolsraised, table at X_(O) and Y_(O), substrate under suction, nitrogenpresent, machine on automatic, as indicated in FIG. 21). Anunsatisfactory condition is indicated to the operator and the program iscaused to check again the initial conditions after correction made bythe operator. If the initial conditions are satisfactory, the firstphase of the cutting sequence is initiated.

A selection of the working station is made after the initiation of thecutting sequence or after a re-initiation (C) subsequently performed, asshown in FIGS. 22 and 24.

Upon selection of the working station, the table 52 and the plate 54 arerespectively positioned in X and Y directions and the film is advanced.The program then arrives at F and continues as shown in FIG. 23.However, before continuing, details should be given on how the film isadvanced. This step begins at D and ends at E or C as shown in FIG. 22.

With reference to FIG. 22, at D the program questions whether the end ofreel 82 is reached. If not, the program commands the advance of film 22and dispense of nitrogen. It stops the film accordingly and verifieswhether nitrogen is present and the device 18 has a good operation. Anabsence of nitrogen is indicated to the operator and after the supplythereof the program re-commands the dispense of nitrogen. If a device 18is found unsatisfactory, the program recommands the advance of film 22and dispense of nitrogen. However, if the device is satisfactory, themonitor program commands the stop of nitrogen. The program now arrivesat E.

If the end of reel 82 is reached, a message is transmitted to theoperator for indicating where a reel is run out.

As previously mentioned, the monitor surveys the state of all the headsof the bank 46 for finding a reel 82 not run out and having a same typeof device 18, and a head compatible. If a station is available, amessage is transmitted to the operator for indicating that the stepfollows through the station available referred accordingly. If theavailable station is a new station, the cutting sequence is modified andhas to be re-optimized. However, if the available station is not a newstation, the cutting sequence is maintained.

The cutting sequence continues by checking that types of device presentat start or still present at stations yet to be used. If no error isfound, the cutting sequence is re-initiated and continues at C on FIG.21. If errors are found, a message is accordingly transmitted to theoperator and the program surveys the types of device present. Thecutting sequence runs thus in a loop until no error is found.

The cutting sequence continues at F on FIG. 23. At this point, the toolcan be ordered to descend. This is made while a suction is switched onfor maintaining the device against the tool along the descent path. Thetool speed is monitored before landing on the substrate. If the speed istoo slow, the tool is ordered to stop and a message is sent to theoperator for indicating to him that the speed is too low. If a stop isordered, instructions are given to return to the loading point and tostart again with the next substrate. Otherwise, the program is continuedin causing the tool to be reascended in Z direction to the initial pointZ0, and is returned to F.

If the tool speed is satisfactory, the distance Z is measured between Z0and Z4 (see FIG. 29). Upon passing through Z4, the suction begins to bemonitored. The distance Z is always measured and at Z5, the descent ofthe tool is slowed for beginning the landing. According to the forcefrom the tool, the latter is stopped while an order is given to releasethe device 18. Accordingly, the device 18 dwells on the correspondingarea 16 of the substrate 10. At this point, the program is at G.

Referring now to FIG. 24, it can be seen that after G the tool is raisedagain up to Z0. After that, an incrementation of display at desk is madeand the program questions whether the cutting sequence is completed. Ifno, the next cutting operation is initiated and the program returns to Con FIG. 21. If yes, the program begins the soldering sequence.

The soldering sequence is firstly optimized, in a same manner as thecutting sequence and as lately described. At this point, the program isat H and continues as indicated on FIG. 25.

The first phase of the soldering sequence is initiated and the solderingstation is selected. The selection can also be produced after initiationof a next phase of soldering sequence from I shown in FIG. 28. When theselection is made, the table 52 and plate 54 are respectively positionedin X and Y directions for matching the selected station with acorresponding area 16 of substrate 10. The tool is then ordered todescend and the distance Z is measured. Upon passing through Z5 (FIG.29) the descent of the soldering tool is slowed before landing on thesubstrate. The force from the tool conditions the stop thereof. Theprogram is now at J and continues as indicated on FIG. 26.

The mode of monitoring the soldering operation is selected. Theselection depends on the type of tool. If the tool has no thermocouple,the soldering operation is time monitored, whereas if the tool has athermocouple, it is temperature monitored. Note that the question aboutthe selection is also raised after re-occurence of a soldering generatorincident and repair. For a time monitor, the duration of soldering isselected and the soldering is commanded to begin. The duration ismonitored until command for soldering to end. It is also generated acommand for nitrogen to be dispensed. The cooling time is selected inaccordance with the type of tool and the time is monitored accordingly,the end of cooling is translated by the character K.

If the soldering operation is monitored in temperature, the temperatureat which soldering is to stop (T_(SS)) is selected. Command forsoldering to begin is generated while the temperature is measured. WhenT=T_(SS), the soldering is stopped and nitrogen is caused to bedispensed. The temperature continues to be measured until T is equal tothe temperature T_(d) at which the tool is free to withdraw. Thus, theprogram arrives at K, and continues as indicated in FIG. 27.

At K, a command for the tool to raise is generated and the distance Z ismeasured until Z=Z7 (between Z0 and Z6. A command for the tool to stopis then generated while the program questions whether nitrogen is stillpresent. If no, a corresponding message is sent to the operator. Uponrepair or if nitrogen is still present, a command for nitrogen to stopis generated. After that, the program raises the question: has the finalsoldering temperature been reached ? If no, a message is sent to theoperator and instructions are given for returning to the loading pointwith a view to start again with the next substrate. If yes, the programasks whether the soldering operation at this station is the last one.The tool is raised up to Z0 in the affirmative. In the negative, or whenthe tool is at Z0, the desk display is incremented. The program is nowat L and continues as shown in FIG. 28.

With reference to FIG. 28, if the sequence is not completed, the nextphase of soldering sequence is initiated and the program returns to Iindicated in FIG. 25. If the sequence is completed, a command isgenerated for table 52 and plate 54 to return to X_(o) and Y₀,respectively. When the table and the plate are at X₀ and Y_(o), thesubstrate is released and a message, which mentions that the substratecan be removed, is shown to the operator. When the substrate is removed,a command is generated for "all done". Then the program asks "whatnext?". As illustrated in FIG. 19, if the next substrate is of a newtype, the program returns to A; if the next substrate is of a same type,the program returns to M. and if no substrate is provided, the programis regarded as finished and returns to T.

Details will now be given on how the sequences are dranw up andoptimized.

All the states through which the data passes whilst operations are goingon are shown in FIG. 15, using a simple example which is different fromthat already given above so that the invention can be more completelyillustrated.

Let it be assumed that the substrate is to be equipped with devices ofgiven types 3 and 5 at the points indicated in FIG. 15A. It will beassumed that these devices are available at two stations 4 and 5 whichare represented in FIG. 2 by the positions of the cutting heads 48D and48E. It will also be assumed that the two kinds 3 and 5 of devices 18belong to the same category and are operated on by a soldering head oftype 1 which is located at a station 1 occupied in FIG. 2 by head 48A.

The equipment plan, in its external format, (FIG. 15B) gives for eachposition to be equipped the type of device 18 which is to be installedthere. This list may be in any order whatever. In the monitor program,it will be in the internal format shown in FIG. 15C. Each position to beequipped with a device 18 has associated with it one memory word in thecomputer 200 which consists of the X, Y co-ordinates of the position onthe substrate and a code for the type of device. The relationshipbetween the designations for the positions used in drawing up theequipment plans and the relative X, Y co-ordinates is shown in FIG. 16.The transition from the equipment plan to the cutting and solderingsequences consists in replacing the data (x, y, type of device) given bythe equipment plan by the absolute co-ordinates X, Y for the positionwhich the plate 54 needs to occupy if the x, y position to be equippedis to be situated under the head of a tool containing the requisite typeof device 18 (during the cutting sequence) and under a compatiblesoldering head (during the soldering sequence).

Consideration will now be given to the system of absolute X, Yco-ordinates for plate 54. The monitor knows the position of the plate54 by means of a system of absolute co-ordinates or scales X, Y. The Xscale will first be considered. The various aspects of the X scale areshown in FIG. 17. When the table 52 is moving forward, a scale is usedin which the successive positions in which the table is to stop, arenumbered 1, 2, etc. from the loading point Xo=0.

It has been seen that each row or corridor on a slotted plate has itsown scale, with points in the same serial position not necessarilyoccupying the same physical position. In the case which is now beingconsidered the maximum value of X on the "forward" scale is 8×10=80.

When a table is moving backwards, the scale used is one in which thesuccessive positions in which the table stops are measured from animaginary point on the extreme right of the machine 42, as seen in FIG.2, (Xn=128) and they are numbered 129, 130 etc. Each row obviously hasits own scale for backward movement. From the monitor 's point of view,the forward and backward scales form a single scale with intersectingabscissas. This expedient makes it possible to use the same algorithmfor optimising the equipment sequences whether the table moves forwardsor backwards. The correlations which make it possible to change from therelative x axis position to the absolute X position of the table areillustrated in FIG. 17. As regards the absolute Y scale, the relative yaxis position and the absolute Y position of the table correspond (Y=y).

There will now be described the transition from the equipment plan tothe un-optimised cutting sequence. In all cases, the cutting sequence isalways drawn up and initiated by pre-planning for the table 52 asuccession of movements in the forward direction. In the case of theexample selected, a transition will be made from the equipment plan(FIG. 15C), to the un-optimised cutting sequence (15D), using theequations (1) from FIG. 17, with:

the station 4 address for devices of type 5.

the station 5 address for devices of type 3. It will be noted that inboth tables in FIGS. 14, the various positions to be equipped appear inthe same order. Before being carried out, the cutting sequence isoptimised. The optimising procedure comprises of minimizing the distancetravelled by the table and plate assembly both in the abscissasdirection and in the ordinate direction. Since the two movements areindependent and simultaneous, the X path and the Y path are minimizedindependently of one another.

Consideration will first be given to the X optimisation. In the case ofX, the practical situation which exists is one which simplifies theoperation; the distance between two successive heads (55 millimeters inthe examples selected) is greater than the size of the largest substrateaccepted by the machine (approximately 50 millimeters). As a result, ifthe table 52 is shifted with a movement in a constant direction from oneend of the machine to the other, the substrate which it carries iscompletely clear of one head before arriving under the next head.Consequently, to minimise the X path, it is merely necessary to controlthe table 52 in such a way that it travels from the loading point Xo tothe requisite point furthest to the right in a succession of advances(with halts at the required points), and then to cause it to return toXo in a succession of backward steps (with halts at the requisitepoints).

This result is achieved by arranging the various items in table 15D inorder of ascending value. The result of this arrangement is an optimisedcutting sequence in the X direction. It will be noted that, as a resultof this re-arrangement, all the Y plots which share the same X plot arelikewise in ascending order.

The Y optimisation will be understood by referring to FIG. 18, whichshows the following general case. With a certain X measurement Xo, thelast position YO to be equipped has been equipped. The next positionsare situated at X measurements X1, and then X2. The measurements XO, X1,and X2 not necessarily contiguous. Between the extreme positions Y11 andY1n, there may be any number of positions to be equipped. The sameapplies between the Y21 and Y2n.

To minimise the Y path, the following rules are applied,

(1) If the path (Y0, Y11) < the path (Y0, Y1n), the course will be fromY0 to Y11 . . . Yn.

(2) If the path (Y0, Y11) > the path (Y0, Y1n), the course will be fromY0 to Y1n . . . Y11.

(3) If the two paths are the same, consideration will be given to thesituation on the X2 line.

    ______________________________________                                        (3.1)      the shorter of the        the shorter of                           If         the paths Y11, Y21)                                                                             <       the paths (Y1n,                                     and (Y11, Y2n)            Y21) and (Y1n,                                                                Y2n)                                     ______________________________________                                    

the course will be from Y0 to Y1n . . . Y11.

    ______________________________________                                                   the                       the                                      (3.2)      shorter of the            shorter of the                           If         paths (Y11, Y21)  ≧                                                                              paths (Y1n,                                         and (Y11, Y2n)            Y21)                                                                          and (Y1n, Y2n)                           ______________________________________                                    

the course will be from Y0 to Y11 . . . Y1n.

Bearing in mind the fact that after the X optimisation all the Ymeasurements on the same X line will already be in ascending order, theapplication of the foregoing rules will result either in all the Ymeasurements on the same X line being left in this order or in thisorder being reversed in the equipping sequence. The application of thisY optimisation to the example in FIG. 15A results in the Y measurementscrossed through in table 15E being reversed. As a consequence of thisoptimisation, the devices are cut free and positioned in the orderindicated by the cutting path shown in FIG. 15F.

Whilst the cutting sequence is being carried out, it is altered if atany given moment the reel 82 at the station which is supplying thedevices 18 empties and if the monitor finds identical devices availableat another station either to the right or left of the station which hasemptied. To allow for this new situation, the part of the cuttingsequence which has not yet been carried out is re-evaluated andre-optimised. In cases where the new station is to the left of the oldone, the positions which it has not been possible to equip will be soequipped during the return phase of the table 52 before the solderingsequence. In all cases, the re-optimisation employs the same algorithmas was used for the first optimisation. This operation may be performedrepeatedly with the single proviso that, during the return phase of thetable 52, the monitor program must not look for a replacement cuttingstation to the right of that which has emptied.

After the cutting sequence has been completed, the monitor returns tothe equipping plan (FIG. 15C) and, for each device to be soldered, looksfor the address of a soldering station which has a soldering toolcompatible with the category of the device. In the present example, allthe devices 18 require the same soldering head, which is situated atstation 1. The soldering sequence always takes place during the returnphase of the table 52. The X positions will thus be defined on thereturn scale. By applying equation (2) in FIG. 17 with the address ofstation 1 a change is made from the equipment plan (FIG. 15C) to anun-optimised soldering sequence (15G). By applying the optimisingalgorithm to this sequence, an optimised soldering sequence (FIG. 15H)is obtained. To carry out the optimised sequence it is necessary tofollow the soldering path indicated in (FIG. 15I).

The apparatus 40 which has just been described may be subject to manymodifications. As an example, when associated with a circular substrate,the first reference system will preferably be a reference systememploying polar co-ordinates. Similarly, the lines defining the secondreference system associated with the cutting and soldering tools may bedifferent and may be other than straight lines. In addition, the cuttingand soldering may be performed with the same tool without exceeding thescope of the invention. This will be clearly apparent from thepreceeding description.

Broadly speaking, the invention is in no way restricted to theembodiments described and illustrated and in fact covers all means whichform technical equivalents of the means described, as well ascombinations thereof, if these are within the scope of the invention andare made use of in the context of the following claims.

We claim:
 1. Apparatus for mounting a plurality of devices onto asubstrate, each of the devices being characterized within a firstplurality of types according to its function and within a secondplurality of categories in accordance with its dimensions, the substratehaving a plurality of predetermined positions each for receiving adevice of selected type and category, the devices being carried by andtransported to the substrate by a flexible supporting element, saidapparatus comprising:a chassis, a first plurality of cutting toolsmounted on said chassis, each for cutting a device from its supportelement; a second plurality of attaching tools mounted on said chassis,each for attaching a device to a preselected position of the substrate;said first plurality of cutting tools and second plurality of attachingtools being arranged on said chassis with respect to a first referenceline; means on said chassis for conveying devices of each type to acorresponding cutting tool and devices of each category to acorresponding attaching tool; a movable table on said chassis having aplate for supporting the substrate; moving means for moving said tableand said plate with respect to said first reference line; and controlmeans operably connected to said moving means, said cutting tools andsaid attaching tools for controlling said moving means to move saidtable and said plate so as to be correctly positioned with respect to acorresponding one of said cutting tools and a corresponding one of saidattaching tools, and for actuating said corresponding one cutting tooland said corresponding one attaching tool when the preselected positionof the substrate is accurately aligned with respect to each of saidcorresponding one cutting tool and said corresponding one attachingtool.
 2. Apparatus according to claim 1, including a reel mounted tosaid chassis, the flexible supporting element being rolled up on thereel, said reel being arranged to feed flexible supporting element andthe devices carried thereon to one of said cutting tools, and furtherincluding means connected to said control means for advancingincrementally said flexible supporting element in a manner to bring eachdevice on said supporting element successively into line with said onecutting tool.
 3. Apparatus according to claim 2, wherein said supportingelement contains marks associated with those devices that are faulty,and said apparatus further includes means responsive to the presence ofsaid marks for actuating said advancing means to move said supportingelement and faulty device corresponding to the mark past said cuttingtool so that it will not be mounted upon the substrate.
 4. Apparatusaccording to claim 2, wherein there is included positioning meansassociated with said table comprised of slotted means disposed in afixed relationship with respect to the substrate for defining aplurality of slots, and mobile means including a source of radiation anda radiation sensor sensitive to radiation directed from said sourcethrough one of said slots.
 5. Apparatus according to claim 4, whereinsaid slotted means comprises a first member for defining a plurality ofslots and coupled to one of said tools, and said mobile means is coupledto said plate.
 6. Apparatus according to claim 5, wherein said slottedmeans comprises a second member having a plurality of slots therein andcoupled to said table and said mobile means comprises a second radiationsource and a second radiation sensor for receiving radiation directedthrough at least one of said slots of said second member, each of saidsecond radiation source and said second sensor means coupled to saidplate.
 7. Apparatus to claim 5, wherein said sensor means comprisesfirst and second adjoining radiation receiving areas separated from eachother and disposed upon either side of a line which is parallel to thelength of said slots of said member.
 8. Apparatus according to claim 4,wherein said control means includes means for counting the slots in thesaid member in response to the output of said sensor means.
 9. Apparatusaccording to claim 1, wherein said moving means comprises first andsecond electric motors coupled to said table and to said plate,respectively.
 10. Apparatus according to claim 1, wherein said controlmeans includes means for monitoring the force exerted by said cuttingand attaching tools.
 11. Apparatus according to claim 10, wherein saidmeans for monitoring comprises force measuring means, and flexible meanshaving its first end connected to a transmission piece and its secondend connected to one of said cutting and attaching tools, said secondend being connected to said force measuring means.
 12. Apparatusaccording to claim 11, wherein said force measuring means comprises asensor having a fixed part coupled to said transmission piece and amoving part coupled to said second end of said flexible means. 13.Apparatus according to claim 8 wherein said control means comprisesmeans for monitoring the extent of travel of said cutting and attachingtools.
 14. Apparatus according to claim 13, wherein said monitoringmeans comprises a sensor having a fixed part disposed in a fixedrelation to one of said tools and having a moving part connected to saidone tool.
 15. Apparatus according to claim 1, wherein said platecomprises at least three members affixed to said plate and havingrollers mounted rotatively thereon for receiving the substrate. 16.Apparatus according to claim 4, wherein said control means comprisesmeans responsive to said sensor means for determining the minimum pathof movement of the substrate to move each position of the substrate toreceive a device at one of said cutting tools and to attach the deviceat one of said attaching tools.
 17. Apparatus according to claim 2,wherein said control means comprises means for identifying the types andcategories of devices supported by a supporting element as disposed uponone of said reels.